The reason that TSA dude is smiling is cus he's checking out your rack.

USA TODAY — Body-scanning machines that show images of people underneath their clothing are being installed in 10 of the nation's busiest airports in one of the biggest public uses of security devices that reveal intimate body parts.

The Transportation Security Administration (TSA) recently started using body scans on randomly chosen passengers in Los Angeles, Baltimore, Denver, Albuquerque and at New York's Kennedy airport.

Airports in Dallas, Detroit, Las Vegas and Miami will be added this month. Reagan National Airport in Washington starts using a body scanner today. A total of 38 machines will be in use within weeks.

"It's the wave of the future," said James Schear, the TSA security director at Baltimore/Washington International Thurgood Marshall Airport, where two body scanners are in use at one checkpoint.

Schear said the scanners could eventually replace metal detectors at the nation's 2,000 airport checkpoints and the pat-downs done on passengers who need extra screening. "We're just scratching the surface of what we can do with whole-body imaging," Schear said.

The TSA says it protects privacy by blurring passengers' faces and deleting images right after viewing. Yet the images are detailed, clearly showing a person's gender. "You can actually see the sweat on someone's back," Schear said.